Many vehicles are presently manufactured which are provided with one or more removable seats. The seats may be removed from the vehicle should the driver of the vehicle wish, for example, to carry a large or bulky load. Also vehicles are provided with movable seats, to permit the seat position to be adjusted, and other movable components, such as pillar-loop height adjusters for safety-belts.
There is often a requirement for a vehicle seat to incorporate one or more sensor switches which are utilised to control safety devices intended to provide protection for an occupant of the seat in the event that an accident should occur. For example there may be a requirement for a weight-sensitive switch which indicates the presence of an occupant on the seat. Also there may be a requirement for a buckle switch to sense whether the occupant of the seat is, or is not, using a safety-belt. Signals derived from such switches may be essential for the proper control of the deployment of a safety device such as an air-bag. Many other types of switches may be provided to sense parameters relating to the seat and/or the occupant of the seat in very sophisticated cases.
If a vehicle seat is permanently fixed in position, each switch can be connected by fixed wiring to a central control unit which is utilised to control the deployment of safety devices within the vehicle. It is preferred that for diagnostic purposes a resistor should be connected in parallel with the switch so that the status of the wires can be checked from time-to-time without the switch being closed. Thus the resister creates a resistance valve in the switch circuit which can be measured as indicating the proper connection with the circuit despite the switch being in an open condition.
If, however, the vehicle seat is to be a removable seat, it is not possible to utilise fixed wiring between sensor switches within the seat and the central control unit. Whilst, it would be possible to provide a wiring arrangement involving a connector to be connected and disconnected each time the seat is placed in the vehicle or removed from the vehicle, an arrangement of this type is not preferred, since users of the vehicle may well forget to effect the necessary connections. It is, consequently, preferred to use a contactless-transmission of information relating to the status of switches within the seat using, for example, an inductive coupling in the form of a transformer. Even if a vehicle seat is a conventional adjustable seat it may be preferred to use some sort of wireless connection between the seat and the vehicle. For a component such as a pillar-loop with a height adjuster, which may have a sensor to sense the height of the loop, it may be difficult to make a permanent wiring connection when installing the pillar-loop, and again a wireless connection to a sensor in such a pillar-loop may be preferred.
Here it is to be understood that when a switch is provided with a resistor in parallel for diagnostic purposes as described above, what is sensed when the switch is closed is effectively a change in resistance. The circuit goes from a high resistance circuit, with a resistance value equivalent to that of the nominal value of the resistor that is in parallel with the switch to a low resistance circuit.
If there is, however, a contactless-transmission within the circuit as constituted, for example, by a transformer, the coupling factor of the transformer will effect the measured value of the resistance of the circuit. Where, for example, a transformer is constituted by two parts, one being a part on a seat and one being part on the motor vehicle, the actual value of the coupling factor may be unpredictable, and the coupling factor may be relatively low. It is thus very difficult to determine accurately the resistance of the combination of a switch and resistor in a motor vehicle seat when there is a contactless-transmission between the seat and a central control unit.
The present invention seeks to provide an improved movable or removable seat for a motor vehicle.